Manufacture of component with cavity

ABSTRACT

A method for the manufacture of a component having an internal cavity is described. The method comprises; defining an external geometry of the component, defining a core geometry of the component; and using an additive layer manufacturing (ALM) method, building the component from a plurality of layers laid on a first plane. The core geometry is advantageously designed to suit manufacture of the component using an ALM method which involves local melting of powder in a powder bed to form the layers, permitting easy removal of excess powder from the internal cavity.

The present disclosure concerns the manufacture of dual wall componentswhich include cooling holes passing from a hollow core through a wall ofthe component. More particularly, the invention relates to a coregeometry which facilitates the manufacture of such components using anadditive layer manufacturing (ALM) process.

It is known to provide dual wall components using a casting methodwherein a core is held in place during the casting process. The dualwalls are cast around the core which is subsequently leeched from thecast component leaving a cavity between the walls. Cooling holes arethen machined into the walls, connecting the outside with the cavity.Due to manufacturing tolerances in such a process, there is a lack ofcertainty as to the location of corners and end surfaces defining thecavity. To ensure the holes connect with the cavity, they are positioneda distance from the anticipated position of the corners.

Additive layer manufacturing (ALM) methods are known. In these methods acomponent is built up layer by layer until the 3D component is defined.In some ALM methods, layers are created by selective treatment of layerswithin a mass of particulate material, the treatment causing cohesion ofselected regions of particulates into a solid mass. For example, theparticulate is a ferrous or non-ferrous alloy powder and the treatmentinvolves local heating using a laser or electron beam. Specific examplesof such ALM methods include (without limitation); laser sintering, lasermelting and electron beam melting (EBM).

Additive layer manufacturing (ALM) techniques are known for use indefining complex geometries to high tolerances and can be used as analternative to casting. However, such methods are not ideally suited tosome conventionally used core geometries. For example, where the ALMprocess uses a bed of particulate material, it is necessary to removeall the untreated particulate from cavities in the defined component.This is more difficult than leeching and removing a more fluid core in acasting process. Adopting the same core geometries as in a castingmethod can result in un-treated particulate materials becoming stuck inthe bottoms and corners of the core cavity. During subsequent heattreatments, these unwelded powders sinter in place altering the intendeddesign of the component to the possible detriment of the performance ofthe component.

Cast dual wall components are often used in gas turbine engines todefine complex aerodynamic shapes. The casting process and materialsused provide materials with very specific mechanical properties whichneed to be preserved in an environment where they are exposed toextremes of temperature and pressure. Hollow cavities are providedwithin these components and serve to minimise weight, reduce materialcosts and also provide a conduit through which coolant fluids can bedelivered to cool the cast components ensuring that surfaces of thecomponents do not exceed critical temperatures which would affect theirmechanical integrity. The cavities are connected to external surfaces ofthe component by a plurality of small cooling holes through which thefluid passes forming a coolant layer which protects the externalsurfaces. Incomplete evacuation of core cavities in such designs canlead to a failure of the component and so cannot be tolerated.

According to a first aspect there is provided a method for themanufacture of a component having an internal cavity, the methodcomprising;

defining an external geometry of the component,

defining a core geometry of the component;

using an additive layer manufacturing (ALM) method, building thecomponent from a plurality of layers laid on a first plane;

wherein the core geometry includes a main core passage, a channelextending from a first end of the main core passage to an externalsurface of the component, the channel having an axis which is inclinedat a first angle to an axis of the main core passage whereby to definean apex between walls of the channel and the main core passage which isobtuse, the channel axis further being inclined to the first plane; andthe additive layer manufacturing method includes removing excessmaterial from the main core passage via the channel.

The method is well suited to ALM methods which use a powder bed andlocal melting of the powder to define layers. Once the component hasbeen built, excess powder can conveniently by removed by upturning thecomponent, facing the exit of the first channel downwards and allowingthe excess powder to escape through the first channel. The removal stepmay include the use of a vibrating rig.

The first angle can be between greater than 105 degrees, optionallybetween 120 and 165 degrees, for example about 135 degrees. The firstangle can be selected to suit the external geometry and any limitationson where the channel exit is able to be positioned on the externalsurface. The first and second angles may be the same or different.

The channel can be blended into the main core passage with a smoothlycurved join to minimise the possibility of particulates becoming stuckin tight radii within the core geometry. The channel can be proportionedand positioned such that, once excess material has been removed from thecore geometry, the channel can serve a second purpose in the finishedcomponent. For example (but without limitation), the channel might serveas a cooling hole, a location for a fastener or the like. Alternatively,the channel can be plugged after removal of the excess material.

The channel can be straight; alternatively the channel can be curved orserpentine. The channel can be round in cross section but other channelcross sections are possible. For example (but without limitation) thechannel may have a rectangular, ovoid or a non-axisymmetric crosssection.

The core passage can be elongate. The core passage can be devoid ofcorners and tight radii, at least towards the first end and convenientlythroughout the passage. The core passage can be configured to definesloping shoulders extending from the first channel. The core passage mayfurther include a sloped surface at a second end, distal from and facingthe first end. The sloped surface at the second end may be inclined atthe first angle, in parallel with the first channel axis. The slopedsurface is conveniently inclined to the first plane, laid layers of thesloped surface each providing support for the next laid layer as thesloping surface is built. This provides better structural integrity ofthe end wall.

It will be understood that the geometry of the core passage is notcrucial to the method of the invention. For example (but withoutlimitation) the core passage may have a rectangular, ovoid or anon-axisymmetric cross section parallel to the first plane and may haveits longest dimension parallel to the plane. Along its longitudinalaxis, the core passage may be straight, curved or serpentine.

In addition to the first channel, the core geometry might includeadditional channels. In some embodiments, the core includes a pluralityof additional channels extending from an elongate side of the corepassage. For example, one or more of the additional channels may extendorthogonally to the axis of the main core passage. Optionally, anadditional channel is located adjacent to a second end of the main corepassage which is distal from and facing the first end. This can be aparticular advantage where the channels are intended to serve as coolingholes, presenting an opportunity to deliver cooling air across thewidest extend of the component. The additional channels may extendorthogonal to the axis of a wall through which they pass or may beinclined to the orthogonal. The additional channels can be straight,curved or serpentine. The channel can be round in cross section butother channel cross sections are possible. For example (but withoutlimitation) the channel may have a rectangular, ovoid or anon-axisymmetric cross section.

Optionally, a series of channels can be arranged and connected inparallel by connecting holes.

The first plane can be parallel to a longitudinal axis of the main corepassage. Alternatively, the first plane can be orthogonal to alongitudinal axis of the main core passage.

For example, the component can be manufactured from a ferrous ornon-ferrous alloy or a ceramic. The component may be a component for agas turbine engine. The component may include multiple core passages,each core passage having an associated first channel. First and/oradditional channels extending from the core channel may serve as coolingchannels in the finished component.

A component manufactured in accordance with a method of the inventionmay incorporate multiple main core passages. Multiple main core passagesmay be aligned in series and may optionally be connected by through wallchannels.

In another aspect, the invention comprises a gas turbine engineincorporating one or more components manufactured in accordance with themethod of the invention.

The skilled person will appreciate that except where mutually exclusive,a feature described in relation to any one of the above aspects may beapplied mutatis mutandis to any other aspect. Furthermore except wheremutually exclusive any feature described herein may be applied to anyaspect and/or combined with any other feature described herein.

Embodiments will now be described by way of example only, with referenceto the Figures, in which:

FIG. 1 is a sectional side view of a gas turbine engine which maycomprise components made in accordance with the method of the invention;

FIG. 2 is a schematic figure of a dual wall component made in accordancewith prior known methods;

FIG. 3 shows in a first view, a portion of a component and the coregeometry of the component manufactured in accordance with a method ofthe invention;

FIG. 4 shows in a second view, the core geometry of the componentportion of FIG. 3;

FIG. 5 shows in a third view, the core geometry of FIGS. 3 and 4.

With reference to FIG. 1, a gas turbine engine is generally indicated at10, having a principal and rotational axis 11. The engine 10 comprises,in axial flow series, an air intake 12, a propulsive fan 13, anintermediate pressure compressor 14, a high-pressure compressor 15,combustion equipment 16, a high-pressure turbine 17, and intermediatepressure turbine 18, a low-pressure turbine 19 and an exhaust nozzle 20.A nacelle 21 generally surrounds the engine 10 and defines both theintake 12 and the exhaust nozzle 20.

The gas turbine engine 10 works in the conventional manner so that airentering the intake 12 is accelerated by the fan 13 to produce two airflows: a first air flow into the intermediate pressure compressor 14 anda second air flow which passes through a bypass duct 22 to providepropulsive thrust. The intermediate pressure compressor 14 compressesthe air flow directed into it before delivering that air to the highpressure compressor 15 where further compression takes place.

The compressed air exhausted from the high-pressure compressor 15 isdirected into the combustion equipment 16 where it is mixed with fueland the mixture combusted. The resultant hot combustion products thenexpand through, and thereby drive the high, intermediate andlow-pressure turbines 17, 18, 19 before being exhausted through thenozzle 20 to provide additional propulsive thrust. The high 17,intermediate 18 and low 19 pressure turbines drive respectively the highpressure compressor 15, intermediate pressure compressor 14 and fan 13,each by suitable interconnecting shaft.

Other gas turbine engines to which the present disclosure may be appliedmay have alternative configurations. By way of example such engines mayhave an alternative number of interconnecting shafts (e.g. two) and/oran alternative number of compressors and/or turbines. Further the enginemay comprise a gearbox provided in the drive train from a turbine to acompressor and/or fan.

Many components of the gas turbine engine are dual wall components andtheir internal geometry could be adapted to facilitate their manufactureby the method of the invention. For example (but without limitation),components in the turbine sections 17, 18 and 19, or the combustor 16may be manufactured in accordance with the invention. The method is wellsuited to the manufacture of walls and platforms through which coolingair is often distributed to cool components in these sections.

FIG. 2 shows a dual wall component 1 as is known from the prior art. Thecomponent is cast and is provided with a central cavity 2 outlined byelongate side walls 3 and 4. Channels 5 and 6 are machined through thewalls into the cavity 2. The cavity 2 is substantially rectangular incross section with sharp corners. It will also be noted that thejunctions between the machined channels 5 and 6 and the cavity 2 aresharply angled. It will be appreciated that the geometry of the cavity 2and joining channels 5 and 6 is such that it would be difficult tocompletely evacuate any powder trapped in the cavity 2 from thecomponent 1. The geometry of the core is thus not well suited to someALM methods.

FIG. 3 shows a first view of a component suited to manufacture inaccordance with methods of the present invention. The component 31 hasopposing elongate walls 34 and 35 which flank a main core passage 32. Atan end of the core passage 32, a first channel 30 extends at an angle toa longitudinal axis of the main core passage 32. The channel extendsthrough wall 33. An additional channel 36 extends orthogonally to thelongitudinal axis of the core passage 32 and through wall 34.

FIG. 4 shows another view of the core geometry within the component ofFIG. 3. The core geometry has been rotated through 90 degrees about thelongitudinal axis of the main core passage. As can be seen, the corepassage 32 blends into the channel 36 via sloping shoulders 39. Theshoulders 39 are also gently rounded. The channel 36 can be seen to havea sloping length 38 terminating at an exit 37.

FIG. 5 shows the core geometry of FIGS. 3 and 4 in its entirety in atransparent, perspective view. In this embodiment, the core has beenrotated approximately a further 45 degrees around the longitudinal axisof the main core passage 32. It can be seen that the core passage 32 iselongate and has multiple channels 36 equally spaced along one side. Atan end which is distal from the channel 36, the core passage 32terminates in an angled face 40. A component with this core geometry canbe built upwards from a plane which sits below the angled face 40 and isorthogonal to the longitudinal axis of the core passage 32. Excesspowder remaining in the core passage 32 and channels 36 can be removedby upturning the component so that the first channel exit 37 facesdownwards. Removal of excess material can be assisted by shaking,tapping or vibrating the component 31.

It will be understood that the invention is not limited to theembodiments above-described and various modifications and improvementscan be made without departing from the concepts described herein. Exceptwhere mutually exclusive, any of the features may be employed separatelyor in combination with any other features and the disclosure extends toand includes all combinations and sub-combinations of one or morefeatures described herein.

The invention claimed is:
 1. A method for manufacturing a componenthaving an internal cavity, the method comprising; defining an externalgeometry of the component; defining a core geometry of the component;and using an additive layer manufacturing (ALM) method, building thecomponent from a plurality of layers laid on a first plane, wherein: thecore geometry includes a main core passage having an elongated axis, anda channel extending from a first end of the main core passage to anexternal surface of the component, the channel has an axis which isinclined at an obtuse angle relative to an axis of the main core passagesuch that an apex is provided between walls of the channel and the maincore passage, the channel is smaller in cross-sectional area than themain core passage at the apex, the main core passage is configured todefine sloping shoulders extending from the channel where the channelmeets the main core passage at the apex, the channel axis is furtherinclined relative to the first plane, and the additive layermanufacturing method includes removing excess material from the maincore passage via the channel.
 2. A method as claimed in claim 1 whereinthe ALM method uses a powder bed and local melting to create the layers.3. A method as claimed in claim 1 wherein the step of removing theexcess material involves upturning the component such that the channelfaces downward, and agitating the component.
 4. A method as claimed inclaim 1 wherein the obtuse angle of the apex is greater than 105degrees.
 5. A method as claimed in claim 4 wherein the angle of the apexis in a range of 120 to 165 degrees.
 6. A method as claimed in claim 1wherein the channel is blended into the main core passage with asmoothly curved join.
 7. A method as claimed in claim 1 wherein the maincore passage is elongate.
 8. A method as claimed in claim 1 wherein themain core passage includes a sloped surface at a second end, distal fromand facing the first end.
 9. A method as claimed in claim 1 wherein thecore includes a plurality of additional channels extending from anelongate side of the main core passage.
 10. A method as claimed in claim9 wherein the plurality of additional channels extend orthogonally to alongitudinal axis of the main core passage and/or in parallel with thefirst plane.
 11. A method as claimed in claim 8 wherein an additionalchannel is located adjacent to the second end of the main core passage.12. A method as claimed in claim 1 wherein the first plane is orthogonalto a longitudinal axis of the main core passage.
 13. A method as claimedin claim 1 wherein the layers are formed from a ferrous or non-ferrousalloy, or a ceramic.